1. Field of the Invention
The present invention relates to a contactless eddy current brake for cars.
2. Description of the Prior Art
As well known to those skilled in the art, known contact brakes for cars are designed to be operated by hydraulic or pneumatic pressure, thus pressing against the brake disc of a wheel using frictional brake pads and making a car go slow or stop. However, such known contact brakes are problematic in that the brake pads are frictionally abraded due to frictional contact of the brake pads with the brake disc and there exists a time delay while increasing the frictional pressure against the brake disc. Another problem experienced in the known brakes resides in that the brakes have a large volume and fail to effectively brake the wheels while driving a car at a high speed.
In a detailed description, known contact brakes for cars are devices that frictionally press against the brake disc of a wheel, thus making a car go slow or stop. Such contact brakes are designed to convert kinetic energy of rotating wheels into thermal energy using a mechanical friction means prior to dissipating the thermal energy into the atmosphere, thereby performing a desired braking operation. The contact brakes, operated by hydraulic pressure, are typically classified into two types: drum brakes and disc brakes. The known disc brakes individually comprise a plurality of brake pads, which are positioned around both sides of a brake disc integrated with a wheel, and frictionally press against the brake disc when it is necessary to make a car go slow or stop.
FIG. 8 is a sectional view, showing the construction of a typical disc brake. As shown in the drawing, the disc brake comprises two movable pads or inside and outside pads 20 and 30 which are set in a housing 10 while being parallel to each other with a gap being formed between them. A disc 40, which is integrated with and rotatable along with a wheel, is positioned in the gap between the two pads 20 and 30 in a way such that the disc 40 is normally spaced apart from both pads 20 and 30. A cylinder actuator, comprising a piston 50 and a cylinder 60, is positioned at one side of the inside pad 20, with the piston 50 being capable of pressing he two pads 20 and 30 against both sides of the disc 40 using pressurized oil from a master cylinder (not shown). The cylinder 60 of the actuator is provided with an oil port 61 at its end wall for selectively introducing the pressurized oil from the master cylinder into said cylinder 60. A spring 51 is set in an annular groove 52, formed on the interior wall of the cylinder 60, so that the spring 51 normally biases the piston 50 relative to the cylinder 60 in a direction where the piston 50 returns to its original position. That is, when a brake pedal (not shown) is released, the spring 51 elastically forces the piston 50 to return from an operational position to a released position.
When operating a brake pedal while driving a car, a back pressure is formed in the master cylinder, so that the master cylinder out puts pressurized oil. The pressurized oil from the master cylinder is, thereafter, introduced into the cylinder 60 of the actuator through the oil port 61, thus acting on the piston 50. The piston 50 thereby causes the inside pad 20 to instantaneously press against the disc 40. In such a case, the housing 10 also moves to the right in the drawing under the guide of a slide unit (not shown) due to the hydraulic pressure acting in the cylinder 60. Such a movement of the housing 10 causes the outside pad 30 to press against the disc 40, so that the two brake pads 20 and 30 perform a braking operation. When the brake pedal is released, the piston 50 elastically returns to the original position by the restoring force of the spring 51, thus allowing the disc 40 to be released from the two pads 20 and 30.
However, since the above disc brake is necessarily provided with a complex hydraulic system, so that the construction of the brake is undesirably complicated, this results in an increase in the production cost while manufacturing the brakes. Another problem experienced in such brakes resides in that the brakes fail to immediately stop a car, but allow the car to travel a free running distance for a time until the pressurized oil from the master cylinder effectively acts on the piston in the cylinder actuator. This may undesirably cause traffic hazards.
FIG. 9 is a sectional view, showing the construction of a typical eddy current brake used as a retarder. As shown in the drawing, the eddy current brake comprises a stator and a rotor. The stator comprises a coiled solenoid 71 which is supported by an annular frame 70. The above solenoid 71 surrounds a ring 72 which is coupled to a radial arm 73. On the other hand, the rotor comprises a magnetic disc 77, which is made of a magnetic material and is connected to a bent arm 76. The above rotor is firmly locked to an axle using a bolt 78, so that the rotor is rotatable in cooperation with the axle. In order to allow the rotor to be rotatable independently of the stator, both a spline 74 and a bearing 75 are interposed between the rotor and stator.
When activating the above brake while driving a car, the coiled solenoid 71, positioned around the magnetic disc 77, is turned on, thus forming a magnetic flux. The magnetic flux is perpendicularly introduced Into the magnetic disc 77 prior to flowing to another solenoid (not shown) from said disc 77. An eddy current is thus induced in the magnetic disc 77 due to the Faraday's law. A Lorentz force is generated by the relative action between the eddy current and the magnetic flux, thus forming a braking torque. However, such an eddy current brake is problematic in that it is not suitable for being used as a main brake system for cars since the braking torque is too low when a car runs at a low speed.
In recent years, a brake, which uses a liquid having a pressure capable of being variable in accordance with the power of the magnetic field or the electric field and overcomes the problems experienced in brakes using the solenoids, has been actively studied. However, the brakes, using such a liquid, are problematic in that they necessarily use expensive devices and have a complex construction. In addition, it is necessary to propose more effective and reliable brake systems in accordance with an increase in the maximum speed of a car.